Computational Insights into Excited State Properties of Donor/Acceptor Composites Featuring Tetrathiafulvalene and Nanographenes

The excited-state properties of nanographenes (NGs) and their donor/acceptor (D/A) composites consisting of tetrathiafulvalene (TTF) were explored using time-dependent density functional theory (TDDFT). NGs such as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mi>p</mml:mi> <mml:mi>e</mml:mi> <mml:mi>r</mml:mi> <mml:mi>i</mml:mi></mml:mrow> <mml:annotation>$peri$</mml:annotation></mml:semantics> </mml:math> -hexabenzocoronene (HBC) and its chlorinated derivatives served as tunable non-fullerene acceptors, enabling efficient charge transfer (CT) upon TTF attachment. Charge density analyses revealed multiple CT states with hole localization on TTF and electron on NGs. Photoexcitation of the optically bright localized acceptor states ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>LE</mml:mi> <mml:mi>a</mml:mi></mml:msub> <mml:annotation>${\rm LE}_a$</mml:annotation></mml:semantics> </mml:math> ) initiated hole transfer from NGs to TTF, driving the CT process. Marcus theory predicted much faster CT rates between the bright <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>LE</mml:mi> <mml:mi>a</mml:mi></mml:msub> <mml:annotation>${\rm LE}_a$</mml:annotation></mml:semantics> </mml:math> state and nearby CT states in TTF/HBC-Cl than in TTF/HBC. Anilino substitution at HBC-Cl modulated the electronic structure of TTF/HBC-Cl-A1, enhancing CT rate through strong electronic coupling and optimal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msub><mml:mi>LE</mml:mi> <mml:mi>a</mml:mi></mml:msub> <mml:annotation>${\rm LE}_a$</mml:annotation></mml:semantics> </mml:math> -CT energy alignment. Conversely, para-amine substitution on the anilino units in TTF/HBC-Cl-A2 lowered the electronic coupling, resulting in a 1-2 order decrease in CT rate relative to TTF/HBC-Cl-A1. These findings highlight that NG functionalization effectively modulates CT behavior, guiding the design of advanced optoelectronic materials.